The invention relates to a permeation cell according to the preamble of patent claim 1.
Such a permeation cell is known in that form as a so-called Franz cell, and it is customary for a bell-shaped donor chamber to be placeable on an upright pot-shaped acceptor chamber with a flat stainless steel ring and a sealing ring being placed between them, the donor chamber having a filling tube that ends inside it in a bell and the acceptor chamber having a tube that emerges upwards from the side at an angle for taking samples manually. A membrane in the form of a skin specimen must be stuck onto the stainless steel ring and then the above-mentioned parts of the Franz cell must be stuck sealingly together. Such a construction is relatively complicated to manipulate and also has the disadvantage that, as a result of degassing of the acceptor medium, gas bubbles collect on the underside of the membrane, as a result of which the diffusion of the active ingredient from the donor region is disturbed and substantially fluctuating permeation results are produced.
A permeation cell has already been proposed in which the membrane extends vertically during operation and the acceptor chamber can be inserted by means of two connection pieces into a so-called HPLC (high pressure liquid chromatography) apparatus or the like for automatic evaluation. In addition, inside the acceptor chamber there is a magnetic stirring rod that can be rotatably driven by means of an external magnetic stirring device. In that construction, however, an irregularly shaped donor chamber is attachable around a window opening on the likewise irregularly shaped acceptor chamber by means of a frame and a locking screw, resulting in a construction that is complicated and in turn difficult to manipulate. Moreover, the acceptor chamber has a relatively large dead volume, so that controllable flow conditions at the membrane cannot be obtained without difficulty.
On that basis, the problem underlying the invention is so to construct a permeation cell having the features of the preamble that it is as simple to construct as it is to manipulate and avoids the collection of gas bubbles at the membrane. It should also be possible to obtain predictable uniform flow conditions at the membrane.
The problem is solved essentially by the characterising features of claim 1. In addition, the dependent claims give advantageous construction options.
The construction in question of the acceptor chamber in the form of an upright cylindrical vessel having a side window opening in the region near its base, the enclosure of the acceptor chamber in a housing that fits closely around it and the construction of the donor chamber in the form of a connection piece that can be screwed onto the cylindrical acceptor chamber radially thereto yield a permeation cell having a vertical membrane and low dead volumes in both chambers that is as easy to manufacture as it is to use. Moreover, the construction of the housing in the form of an essentially parallelipipedal block according to claim 10 facilitates the economical use of several such permeation cells next to one another in a hot water bath with a stirring plate or the like.